The research proposal is concerned with aspects of the lipid metabolism of plasma lipoproteins and the lipoproteins of erythrocyte membranes. The proposed investigations are based on the premise that knowledge of lipid-protein affinity in these systems is essential for an understanding of the transport and metabolism of lipids, the structure and function of membranes, and diseases such as atherosclerosis and hemolytic anemia which result from derangement of these lipoprotein systems. By encompassing both circulating and membrane bound lipoproteins the proposed studies will permit comparison of lipid-binding processes in two diverse systems and set the stage for meaningful studies of the transfer of lipids between circulating and membrane-based lipoproteins. The study will be divided into three parts: (1) The isolation and characterization of apolipoproteins. With the exception of the major protein of low density lipoproteins B-protein) the isolation and characterization of the plasma apolipoproteins is already at an advanced stage of development. Only a few of the many erythrocyte membrane proteins are similarly well studied. B-protein and lipid-binding membrane proteins will be isolated and their physical, chemical and functional characteristics determined. (2) Lipid-protein interactions: Our goal is to determine the specific chemical interactions involved in the binding of lipids, especially phospholipids, to the plasma and membrane apolipoproteins. We will initially focus on the high density apolipoprotein apoLp-Gln-II as a model lipid-binding protein. Subsequently other plasma and membrane apoproteins will be employed. Lipid-binding will be assayed by 4 different procedures. The effect of variation of various parts of the lipid molecules will be assessed to determine the specific characteristics of the lipid ligand required for binding. The effect of pH, ionic strength, temperature and D2O on phospholipid-protein interactions will be examined to assess the relative contributions of hydrophobic and electrostatic interactions. Changes in the physical properties of proteins and derivatized lipids that result from lipid-binding will be measured. Various procedures will be employed to identify "lipid-binding sites" in the apoproteins.